The present invention relates to an MOS power structure equipped with a protective device against overvoltages together with the related manufacturing process.
An MOS power structure consists of one or more elementary MOS cells and a parasitic bipolar transistor transistor operating as a diode between the source and drain electrodes of the MOS cell.
It is known that structures of this type require adequate protection for the gate and drain electrodes. The need to protect the gate is the consequence of the fact that the structure is of the metal-oxide-semiconductor type and the voltage which said structure can withstand depends on the thickness of the oxide.
In the power MOS this thickness is very small, i.e. on the order of a few hundred angstroms, and hence the maximum voltage applicable is a few tens of volts. At higher voltages there is a discharge into the oxide with resulting destruction of the component. During dynamic operation there can however exist inlet voltage transients or peaks, depending on the application circuit, which exceed the breakdown voltage of the oxide.
Protection of the drain is necessary because when the component is working in commutation it is subjected simultaneously to high voltages and currents which during the extraction phase cause reverse secondary breakdown stresses and/or harmful volage transients.